The turnover of collagen and associated noncollagenous protein in renal glomeruli will be studied in normal and diabetic rats. The purpose of the study is to ascertain whether or not the accumulation of collagen in diabetic microangiopathy is based on accelerated synthesis or delayed catabolism of glycoprotein. A kinetic study of protein turnover in vivo for up to 48 hours will be done by injecting the rats with 14C-proline and maintaining the radioactivity of the free proline pool by subcutaneous implantation of an osmotic minipump from which 14C-proline is gradually absorbed. Incorporation of label into protein-bound hydroxyproline will be taken as an index of collagen synthesis, and incorporation into bound proline as an index of both collagenous and noncollagenous protein synthesis. The question of increased or decreased turnover will also be approached by a double isotope procedure, in which 14C-proline is injected 4 days and 3H-proline is injected 4 hours, or 1 day, before sacrifice, and 3H/14/C ratios calculated in bound proline and hydroxyproline. In another approach, rats will be injected with 3H-proline and sacrificed 4 weeks later. If differences in turnover are found between normal and diabetic rats, the role of growth hormone will be evaluated by using, as additional experimental animals, hypophysectomized diabetics and hypophysectomized rats injected with growth hormone.